Alumina-chromium cermets by hot-pressing of nanocomposite powders

Alumina-chromium cermets with up to 36 vol% metal have been prepared from powders obtained by high energy ball-milling. Firstly, the powder is prepared from initially blending Cr2O3 or CrO3 and Al for reactive milling and from Al2O3 and Cr for a direct milling. The materials as-pressed at 1400 degrees C under 30 MPa consist of an alumina based matrix with metallic Cr inclusions. The difference of reactivities between Cr2O3 and CrO3 during milling on the final material is discussed and the advantages of reactive compared to direct milling are emphasised. in a second part, the more efficient technique is used to obtain cermets with different compositions. Nanostructured powders were synthesized from Cr2O3, Al and Al2O3. The influence of chromium metal content is studied by microstructural observations, physical, mechanical and electrical properties evaluations. The expected improvement of mechanical properties compared to pure alumina is indeed observed. The importance of the milling rime and the temperature-pressure cycle during the forming and sintering process are reflected on the final material structure and properties. (C) 1998 Elsevier Science Limited. All rights reserved.